1. Field of the Invention
The present invention relates to an apparatus for and a method for calibrating a resistance thermometer, particularly a resistance thermometer of the type having a thermally sensitive resistance element in operable connection with a bridge measurement circuit used to measure gas temperatures in a gas composition analyzer.
2. Description of the Prior Art
Resistance thermometers, for example ones employing a thin platinum wire as a thermally sensitive resistance element, are well known in the art. The electrical bridge circuit to which such an element is operably connected usually configured so that a thermally induced electrical resistance change of the resistance element produces a linearly dependent change in an electrical parameter of the circuit, such as voltage or current. This parameter is then supplied as a measure of the temperature sensed by the resistance element.
In order to ensure that the resistance thermometer provides an accurate indication of a temperature to be measured it should be calibrated at least once, preferably on a number of occasions, during its operation. The typical calibration procedure which is followed is a multi-point, normally two point, calibration where the output from the bridge circuit is recorded at several known reference temperatures. Often a calibrated reference thermometer is located in thermal contact with a system, the temperature of which is to be monitored by the resistance thermometer, and used to provide the reference temperatures against which the resistance thermometer is calibrated.
Such a calibration procedure, even using only two points, is not trivial since the system, the resistance element and the reference thermometer must be allowed to come into thermal equilibrium before each calibration point is recorded. This results in a relatively lengthy calibration procedure.